1. Field of the Invention
The present invention relates generally to the fields of bacteria, antimicrobials and antibiotics. More particularly, it provides novel methods, kits, and combinations of antimicrobial agents and inhibitors, for use in reducing the resistance of bacteria and other microorganisms to antimicrobial agents. In particular, the invention provides for enhanced bacterial killing using a macrolide, lincosamide and streptogramin B (MLS) antibiotic in combination with an agent that inhibits methylation, as exemplified by inhibiting methylation or maturation of bacterial RNA.
2. Description of the Related Art
The first antibiotics were used clinically in the 1940s and 195s, and their use has been increasing significantly since this period. Although an invaluable advance, antibiotic and antimicrobial therapy suffers from several problems, particularly when strains of various bacteria appear that are resistant to antibiotics. Interestingly, bacteria resistant to streptomycin were isolated about a year after this antibiotic was introduced (Waksman, 1945).
The development of antibiotic resistance is a serious and life-threatening event of worldwide importance. For example, strains of Staphylococcus are known that are immune to all antibiotics except one (Travis, 1994). Such bacteria often cause fatal hospital infections. Among other drug resistant organisms are: pneumococci that cause pneumonia and meningitis; Cryptosporidium and E. coli that cause diarrhea; and enterococci that cause blood-stream, surgical wound and urinary tract infections (Berkelman et. al., 1994).
Davies (1986) described seven basic biochemical mechanisms for naturally-occurring antibiotic resistance: (1) alteration (inactivation) of the antibiotic; (2) alteration of the target site; (3) blockage in the transport of the antibiotic; (4) by-pass of the antibiotic sensitive-step (replacement); (5) increase in the level of the inhibited enzyme (titration of drug); (6) sparing the antibiotic-sensitive step by endogenous or exogenous product; and (7) production of a metabolite that antagonizes action of inhibitor.
Certain bacteria become resistant to antibiotics by utilizing ribosomal mutations (Cunliffe, 1990), although some reports have stated that this type of resistance is of doubtful clinical significance (Spratt, 1994). Ribosomal mutations result in bacterial resistance to macrolide, lincosamide and streptogramin B (MLS) antibiotics, as has been observed in the resistance of various Staphylococcus, Streptococcus, Enterococcus, Bacillus and Mycoplasma strains to important antibiotics such as erythromycin (LeClercq & Courvalin, 1991).
The induction of erythromycin resistance generally leads to bacterial strains that express rRNA which does not bind to this type of antibiotic. Mainly, erythromycin resistance is due to the induction by macrolides of a methylase protein, which catalyzes the methylation of the binding site of erythromycin on the rRNA, thus preventing antibiotic binding. Despite intensive studies in this area, there remains few, if any, practical proposals as to how bacterial resistance to MLS antibiotics may be overcome.